Keeping the temperature of a mobile communications and computing device, such as a smartphone or tablet computer, with multiple processing units (PUs) under control is an area of concern for several reasons. One reason is that leakage current in a PU increases as temperature increases, thereby draining battery resources. A second reason relates to device preservation and user safety. For example, in some scenarios temperature can keep increasing to the point that the device not only reaches a point of failure wherein internal circuitry starts to malfunction but the device can also become hot enough to cause discomfort to a user. Accordingly, thermal mitigation is a long-standing issue that seeks to keep device temperature under control while maintaining satisfactory performance.
One technique for performing thermal mitigation is to reduce voltage supplied to one or more PUs in a mobile device. Reducing voltage to a PU reduces power consumption which in turn reduces an amount of heat produced by the PU. A PU may be designed to operate at a lower speed, for example, as voltage is reduced, thus providing for a tradeoff between power consumption and performance.
Digital circuits are usually integrated on semiconductor dies, and several PUs, such as a modem and a multi-core processor, may be present on a single semiconductor die in a mobile device. A system on chip (SoC) refers to multiple PUs embedded on a single die. A PU is a functional block on the SoC. For example, a PU may be a wireless baseband modem, a graphics processing unit (GPU), an image processing unit, a core in a multi-core processor, or other type of processing circuitry.
The PUs in an SoC may encompass a wide variety of functional elements, and thus, their frequency and voltage requirements (e.g., related to desired performance) may differ vastly at any given moment. Therefore, in order to adequately perform thermal mitigation, one or more of these functional blocks may be independently operated such that their respective frequency and voltage values may be appropriately scaled. In general, a voltage source controls the power supplied to a PU, and thus a voltage source is a type of power supply.
However, operating the multiple PUs independently at individual voltages and frequencies may require a plurality of power supplies and corresponding voltage rails. Generally, any number of PUs can be supplied by any number of power supplies. There are at least as many PUs as power supplies, and in some scenarios each PU has its own power supply. The power supplies may be located off the SoC, resulting in excessive cost and/or pin count. A switched mode power supply (SMPS) is one such example. In some conventional mobile device architectures, multiple SMPSs are part of a power management integrated circuit (PMIC).
In other embodiments, at least one of the independent power supplies may be located on the SoC, but the power supplies are sized such that power is supplied to all cores, and as a result occupy a large area of the die. There is therefore a need for mobile device architectures and methods that provide adequate thermal mitigation without incurring excessive penalties for cost or die area.